The present invention relates to an electronic endoscope system which detects an image of an object using an imaging device, processes the detected image, and outputs the processed image to a monitor for viewing.
In the conventional electronic endoscope system, an image of an object (such as an internal organ or tract of the human body) is formed by an optical system on an imaging device, such as a CCD. The imaging device outputs an electrical signal to a video processor. The video processor processes the signals and outputs a video signal to the monitor in order to display the image detected by the electronic endoscope system.
FIG. 1 shows a conventional electronic endoscope system having an endoscope insertion portion 50 and a video processor 60. The endoscope insertion portion 50 has an imaging device such as a CCD 51 for detecting an image of an object. Light from a light source 66, located in the video processor 60, is transmitted, through an aperture 67 and a fiber optic cable 52, towards the object to be viewed. A light transmitting area of the aperture 67 is adjusted (i.e., the size of the aperture is changed) by an aperture drive circuit 65.
The image of the object is formed by a lens 55 on the CCD 51. Then the CCD 51 outputs an image signal to a first signal processing device 61 of the video processor 60. The image signal is processed and then transmitted to a second signal processing device 62, which converts the processed image signal to a video signal such as the NTSC signal that is then displayed on the monitor 80.
The processed image signal output from the first signal processing device 61 is also transmitted to one of a peak value detecting circuit 63 and an average value detecting circuit 64. An operator manually selects the peak value detecting circuit 63 or the average value detecting circuit 64 using an operation panel 69. A CPU 68 receives an operation signal from the operation panel 69 and operates switches 71 and 72 to select either the peak value detecting circuit 63 or the average value detecting circuit 64.
The aperture control circuit 65 controls the size of the aperture 67 in accordance with a signal output from the peak value detecting circuit 63 or the average value detecting circuit 64. Therefore, the size of the aperture is adjusted in accordance with the processed image signal, in order to maintain uniform average or peak brightness of the observed image.
However, with the electronic endoscope system described above, the operator must manually select the type of processing that will be performed on the image signal in order to control the size of the aperture 67. This reduces the efficiency of the electronic endoscope system and increases the burden on the operator as well as the patient who is being observed with the endoscope system.
Further, in the conventional electronic endoscope system, if there is a portion which is much brighter than the other portion within the observed area, the brightness of the brighter portion affects the average brightness of the observed area. In such a case, the aperture may be closed greater than necessary, and the other portions may not be observed because sufficient light is not received from such an area even if the average brightness has been unchanged.
Still further, even if the amount of light emitted from the fiber optic cable is the same, the average brightness of the observed area changes depending on the type of the CCD, magnification of the image, and the like.
Further, if the video processor 60 of the electronic endoscope system is designed to be used with a monitor of a TV system, such as NTSC, having a certain frame rate, and it is then used with a monitor of another TV system, such as PAL, having a different frame rate, it is necessary to change circuits. For example, a capacitor which controls a time constant of the peak value detecting circuit 63 and the average value detecting circuit 64 must be exchanged with a capacitor having different characteristics which are appropriate for the other system. Therefore, the size of the circuit must be increased to accommodate the extra capacitor, if the adaptability of the electronic endoscope system to operate with different monitors is required.